Thesis (M.Sc.) - Cairo University - Faculty of Oral and Dental Medicine - Department of Prosthodontics

This in vitro study was carried out to assess the shear bond strength of composite resin bonded to enamel and dentin pretreated with acid etchant and Er, Cr : Ysgg. Non carious 66 sound human premolars were selected to prepare 132 specimens for this study. Buccal surfaces were flattened and were ground under copious water coolant to obtain a flat enamel surface while the lingual surfaces were ground to obtain a uniform flat surface of superficial dentin. Subsequently, the surfaces were polished with 240 grit, 400 grit and 600 grit sandpaper disks to standardize the smear Layer. Prepared specimens were randomly divided into two main groups, 66 specimens each, according to etching methods (A); group (A1) etching by an Er, Cr : YSGG laser system (waterlase MD, biolase); and (A2) etching by phosphoric acid using scotchbond universal etchant. Each group was further divided into two subgroups 33 specimens each according to tooth substrate tested (S); where (S1) was for enamel, while (S2) was for dentin. Each subgroup was divided into three classes 11 specimens each according to storage time (T); stored for 1 day (T1), stored for 7 days (T2) and stored for 30 days(T3). The adhesive was applied on the substrate and cured then a plastic tube (Tygon tube), 0.7 mm in diameter and 1mm in length was held securely and immobilized using cotton pliers on the indicated substrate. Then resin composite (Z 350 XT) was packed into the tube and cured. Microshear bond strength test was conducted using universal testing machine at crosshead speed of 0.5 mm/min till specimens fail, bond strength was calculated in MPs

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